BC127 Melody 7.2 – PCM Audio Unintelligible


#1

Our product incorporates your BC127 Bluetooth module as audio gateway for Iridium 9523 Voice Transceiver with PCM master clock 2048 kHz, and 8 kHz frame sync.

The Melody 6.1.5 version provides good audio quality but with issues controlling audio volume.

We have tried to upgrade to Melody 7.1 and 7.2 but the audio is unintelligible.

I have reproduced this unintelligible audio with Melody 7.2 on your Discovery Board.

The issue appears to be associated with Auto-adjust digital rate setting.

The Iridium 9523 operates only at 8 kHz (125 uSeconds) Voice Audio Rate.

Test Setup Using - BC127 Discovery Board v2 No Co Processor

  1. Load Melody 7.2 into Discovery Board

  2. Select PCM Audio - J6 Grounded (pin 2 to 3)

  3. Jumper PCM_OUT to PCM_IN J4 (pin 3 to 4)

  4. Configure Digital Audio - BC127 as PCM Master

  5. Connect Bluetooth Headset

  6. Establish Headset Audio Path

Configuration One: SET AUDIO_DIGITAL=1 8000 2048 2500020 ON

Observed Sync Rate (PCM_SYNC) - 62.5 uSeconds

Observed Clock Rate (PCM_CLK) - 2048 kHz

Audio Quality - Very Good

Configuration Two: SET AUDIO_DIGITAL=1 8000 2048 2500020 OFF

Observed Sync Rate (PCM_SYNC) - 125 uSeconds

Observed Clock Rate (PCM_CLK) - 2048 kHz

Audio Quality - Unintelligible


#2

Hi,

So config 1 and 2 you have run on 7.2 and 1 works where 2 does not?

We do not play with PCM as it comes straight out of the chipset (as you can see there is nothing we have actively changed in the release notes).

Regards

Matt


#3

I have read the release notes for version 7.1 and 7.2 and expected them to behave consistent with version (6.1.5). Both Configuration One and Two with the exception of the last parameter enable_auto_rate (not implemented in 6.1.5); product good quality audio. The digital rate (2nd) parameter in the AUDIO_DIGITAL should define the frame sync rate for PCM audio. I also noticed that setting the 16000 rate produces an Error Code 0x0013 (wrong parameter).


#4

Some additional clarification:

Melody (6.1.5) – Configuration’s

Configuration One: SET AUDIO_DIGITAL=1 8000 2048 2500020

Observed Sync Rate (PCM_SYNC) - 125 uSeconds

Observed Clock Rate (PCM_CLK) - 2048 kHz

Audio Quality – Unintelligible

Configuration Two: SET AUDIO_DIGITAL=1 16000 2048 2500020

Observed Sync Rate (PCM_SYNC) - 62.5 uSeconds

Observed Clock Rate (PCM_CLK) - 2048 kHz

Audio Quality - Very Good


#5

Some additional clarification:

Melody (6.1.5) – Configuration’s

Configuration One: SET AUDIO_DIGITAL=1 8000 2048 2500020

Observed Sync Rate (PCM_SYNC) - 125 uSeconds

Observed Clock Rate (PCM_CLK) - 2048 kHz

Audio Quality – Very Good

Configuration Two: SET AUDIO_DIGITAL=1 16000 2048 2500020

Observed Sync Rate (PCM_SYNC) - 62.5 uSeconds

Observed Clock Rate (PCM_CLK) - 2048 kHz

Audio Quality - Very Good


#6

@BlackWolf,

So it seems to me that neither 6.1.5 or 7.2 firmware like the 16KHz frequency you are trying to send to it as they both return ERROR 0x0013.

6.1.5 firmware

version
BlueCreation Copyright 2017
Melody Audio V6.1.5
Build: 1496939390
        Bluetooth address 20FABB075D3F
        Profiles: A2DP AVRCP HFP BLE SPP PBAP MAP
        Codecs: SBC
OK
SET AUDIO_DIGITAL=1 8000 2048 2500020
OK
SET AUDIO_DIGITAL=1 16000 2048 2500020
ERROR 0x0013
SET AUDIO_DIGITAL=1 8000 2048 2500020
OK
SET AUDIO_DIGITAL=1 16000 2048 2500020
ERROR 0x0013

7.2 firmware

version
Sierra Wireless Copyright 2018
Melody Audio V7.2
Build: 1534785311
    Bluetooth addresses: 20FABB075D0B 5CF8AFC1D837
    Profiles: A2DP AVRCP HFP BLE SPP PBAP MAP TWS
    Codecs: SBC
OK
SET AUDIO_DIGITAL=1 8000 2048 2500020
OK
SET AUDIO_DIGITAL=1 8000 2048 2500020
OK
SET AUDIO_DIGITAL=1 16000 2048 2500020
ERROR 0x0013
SET AUDIO_DIGITAL=1 16000 2048 2500020
ERROR 0x0013

Regards

Matt


#7

We have been using the following setting for over two years with the previous versions of Melody firmware including version (6.1.5).

SET AUDIO_DIGITAL=1 8000 2048 500020

BC-127:

Slave Mode PCM

Enable PCM Short Synchronization

16 bits in 16 cycle slot duration

PCM Slot One

Our voice modem produces 8 KHz Audio with 2048 KHz master clock.

We do have an issue with the inability to independently control the incoming and outgoing volume level. The separation of volume control was to be implemented in Melody (7.2). We have been unable to produce usable audio with the new version code.